so your engine revs but nothing happens if I am correct do this,
go thru your system , first engine drives the clutch, clutch shoes are engaging properly(springs are not to stiff?), pinion to spurs are meshed correctly yes? spurs are driving the main rear shaft which is connected to your belt yes? rear belt is not to loose?? then after that could be your diff is stripped inside??? then after that and highly unlikely check you universals/dogbones. this should find your problem.
cheers.
